Field of the Invention
The invention relates to an impact detection device, in particular for a motor vehicle, including at least one micromechanical acceleration switch having a contact element to be moved as a function of acceleration and a counter-contact element. A monitoring circuit, which is electrically conductively connected to a terminal of the contact element and to a terminal of the counter-contact element, has a controllable voltage source and an evaluation device. The impact detection device has an operating state for detecting an impact, in which a voltage is fed to the terminals by the voltage source.
European Patent Application 0 567 938 A1, corresponding to U.S. Pat. No. 5,610,337, has disclosed an impact detection device which has at least one acceleration switch that has a micromechanical structure. Such an acceleration switch essentially contains a contact element which can be moved as a function of acceleration, as well as a counter-contact element. When a defined acceleration is exceeded, the contact of the acceleration switch closes. A monitoring circuit is electrically conductively connected to terminals of the contact elements. A voltage is fed to the terminals in order to detect an impact (see FIG. 1c of European Patent Application 0 567 938 A1, corresponding to U.S. Pat. No. 5,610,337).
In order to test and reset the micromechanical switch, a test electrode is provided which is electrically connected through a separate conductor to the monitoring circuit and which is driven by the monitoring circuit (see FIG. 3a of European Patent Application 0 567 938 A1, corresponding to U.S. Pat. No. 5,610,337). In particular, if the monitoring circuit and the acceleration switch are spatially separated from one another, a line with at least three conductors is necessary between the acceleration switch and the monitoring circuit. The line is provided, on one hand, in order to be able to detect an acceleration-dependent closure of the acceleration switch in the monitoring circuit and, on the other hand, in order to be able to test or reset the acceleration switch through the use of the monitoring circuit.